Black Bears, Other Wildlife Begin Preparing for Winter Hibernation

Wisconsin Black BearSPOONER, Wis. – As temperatures drop and snow flurries begin to fly in November, some Wisconsin wildlife animals begin looking for spots where they can avoid the cold by either hibernating or enter a long winter’s sleep.

State wildlife officials say that there are generally two kinds of winter sleepers: true hibernators and “light sleepers.”

“Both styles help animals and some reptiles endure the winter,” says Gary Dunsmoor, a Department of Natural Resources wildlife technician in Spooner. “And both most likely have a lot to do with food availability — just as many species of wildlife migrate for the winter months due to lack of food here, many animals likely hibernate for the same reason.”

Dunsmoor says true hibernators like bats, woodchucks, and ground squirrels “sleep so deeply, it is almost impossible to wake them.”

A woodchuck’s heart rate, he notes, goes from 80 beats a minute when active to four to five beats a minute in hibernation. Other true hibernators include snakes, turtles, and frogs. Frogs and turtles bury themselves in the mud below the frost line getting oxygen from air trapped in the mud. Some snakes head underground while others gather together in sheltered places like rotted logs.

Dunsmoor says bears, skunks, raccoons, opossum and badgers are “light sleepers.”

“These characters can be awakened from their winter nap. They breathe a little more slowly and lower their body temperature a few degrees during sleep but will awaken to feed.”
 
Black bears in Wisconsin usually begin looking for places to make their dens by mid-October, Dunsmoor says, but warm weather or a healthy acorn crop will keep them active into November. Bears generally make dens in shallow holes near overturned stumps or blown-over trees, in shallow caves, in hollowed-out trees or in rock crevices. However, Dunsmoor says, some bears take only a low spot on the ground with plenty of leaves to sleep on.

While scientists are not sure how or why animals go into hibernation, Dunsmoor says they have found a special substance in the blood of hibernators.

“It is called Hibernation Inducement Trigger. If blood is taken from a hibernating squirrel in the winter and injected into an active squirrel in the spring, the active squirrel goes into hibernation,” he says..

What biologists also know is that hibernators put on a special kind of fat known as brown fat. This special fat is found across the back and shoulders of hibernating animals, close to their organs like the brain and liver. Brown fat delivers quick energy to an animal coming out of hibernation.

Dunsmoor says wildlife watchers can see hibernators out foraging for foods now in attempt to put on as much fat as possible because they will not eat much when the snow flies.

Come the snow when outdoor adventurists are cross country skiing, snowmobiling and snowshoeing they will probably be passing by hibernators without knowing it.

“Snows provide insulating warmth and cover. They won’t hear them either, most hibernators, don’t snore,” Dunsmoor notes.

FOR MORE INFORMATION CONTACT: Gary Dunsmoor – (715) 635-4092


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